Aminoglycosides are drugs used in the treatment of several bacterial infections that are potential agents of bioterrorism. Their therapeutic value is derived from their ability to specifically recognize prokaryotic 16S rRNA A-sites and interfere with protein synthesis. The goal of this proposal is to define the molecular forces that dictate the specificities of aminoglycosides for prokaryotic versus eukaryotic A-sites, as well as to investigate whether mitochondria! A-sites serve as targets for these drugs. Binding to the latter target has been implicated for the basis of the adverse effects associated with aminoglycoside treatment. In addition, a fluorescent-based approach will be employed to evaluate the impact of aminoglycoside binding on the conformational dynamics of rRNA A-sites to test the model that invokes a drug-induced conformational change in the rRNA as being a key factor in the ability of the drugs to cause aberrant translation. The proposed studies will reveal critical determinants for the prokaryotic specificity of aminoglycosides, as well as enhance our understanding of molecular mechanism by which aminoglycosides inhibit protein synthesis. This information is valuable for the development of a rational basis for future antibiotic design.